In this research application the cell kinetic profile of surgically resected individual human colorectal tumors will be made at time of removal from the patient. Explants of these tumors will be made into nude mice and their kinetic properties determined in two successive transplants thereafter. The kinetics of the explants will be compared to original primary tumor kinetics to determine if alterations have occurred. This information could be extremely important since the ultimate significance of utilizing xenografts as human tumor models depends largely on the extent to which they duplicate the kinetics and response characteristics of the primary tumor. In addition the cell kinetic information obtained on the patient material will add to the data base being established in these laboratories for human colorectal tumors.